1. Field of the Invention
The present invention relates to a cooling system for use with an electronic device.
2. Related Arts
Semiconductors for use in electronic devices, particularly semiconductors represented by CPUs for information processors have achieved rapid progress. It is common knowledge that the semiconductors are subjected to ever-increasing packing density, and generating more heat. Accordingly, it has become a practice to mount a larger number of fans or to increase fan speed to provide adequate cooling of the electronic devices such as semiconductors. Hence, the noise level and power consumption of the electronic devices are on the increase. Since an increasing number of electronic devices are installed at offices and the like, there is a stronger demand for lowering the noise level of the electronic devices. Furthermore, a demand for power-saving feature is increasing from the standpoint of environmental load reduction.
The development of high efficiency cooling technology is required to meet such demands. Now, efforts are made to develop high efficiency fans and high performance heat sinks and to improve cooling structures (refer, for example, to JP-A Nos. 2000-277956, 2009-123887 and 2011-3571).
It is known that in a multifunction electronic device incorporating, in one frame, a plurality of electronic devices operating or functioning independently from each other and one or more fans arranged in series on an air flow passage for collectively cooling some or all of the electronic devices, a cooling air volume for each of the electronic devices disposed in the frame depends upon the air-flow resistance of the flow passage for each of the electronic devices and the capacity of the fan(s). According to the invention disclosed in JP-A No. 2000-277956, a required air volume for cooling is ensured by adjusting the capacity of the fan(s), e.g., increasing the revolving speed of the fan(s), because the air flow passage for the electronic devices exhibits a fixed air-flow resistance. Because of the structure of the multifunction electronic device in which some or all of the electronic devices in the frame are collectively cooled, an excessive volume of air is supplied to some of the electronic devices in order to supply a required volume of air to some other electronic devices. As a result, the fans consume excessive power and generate excessive noises.
According to the invention disclosed in JP-A No. 2009-123887, temperatures of inlet air into and exhaust air from each of the electronic devices are measured, and an amount of temperature rise is calculated from a difference between these air temperatures. The calculated amount of temperature rise is compared with a difference between a predetermined maximum inlet air temperature and a predetermined maximum exhaust air temperature. The volume of air required for cooling the electronic device is adjusted based on the comparison result. However, certain time takes before the variation in the power consumption of the electronic device and the variation in the air volume required for cooling (the variation in the air-flow resistance) are reflected on the temperature variation. Hence, it takes a long time to accomplish the optimization of the air volume required for cooling (optimization of air-flow resistance). Similarly, it takes a long time before the power consumption of the fan(s) is reduced. This makes it difficult for the system to achieve efficient power saving.
According to the invention disclosed in JP-A No. 2011-3571, a frame accommodating an electronic circuit board is formed with a plurality of windows, which are controllably opened or closed based on the temperature of electronic components mounted on the electronic circuit board thereby adjusting the volume of air for cooling the electronic circuit board according to the amount of heat generated by the electronic components thereon. This invention does not pay any consideration to the reduction of power consumption of the fans.